The invention relates to a kiln in which to fire ceramic materials such as tiles and the like.
Such a kiln is intended specifically, though not exclusively, for use in high speed firing processes effected on ceramic materials, and on ceramic tiles in particular. Conventional high speed firing cycles are implemented using continuous roller kilns, in which material is fired while running through from end to end; more exactly, with the kiln operating at regular tempo, a precise distribution of temperature is achieved along the longitudinal axis, from entry to exit.
This temperature appears as a continuous curve exhibiting an initial rise, an intermediate stretch, and a fall. Passing through the kiln, the material is subjected to a steadily increasing temperature while in the pre-heat zone, then to maximum firing temperature, and thereafter, to a relatively gradual cooling; in practical terms, the ceramic material is conveyed along the length of the kiln from entry to exit through a succession of zones, being invested with thermal energy in some, and divested of thermal energy in others. The method most widely adopted in bringing about such exchanges of heat in roller kilns is one based on convection, characterized by the creation of two continuous and colliding flow paths: on the one hand, the ceramic material being fired, which is carried forward into the firing zone by the rollers, and on the other, hot gases which pass from the firing zone out into the flue.
To obtain a given firing curve, different levels of thermal energy are applied in order to produce a break in the effects of the collision for a given space and hold one section of the kiln at constant temperature (the section in which the chemical and physical reactions relative to the firing process proper are allowed to take place).
This basic system of applying heat is beset by drawbacks deriving from the fact that, in passing through the kiln, the material encounters convection currents of dissimilar temperature, direction and rate of flow, and contact with the gases can only be considered nominally uniform at best.
A further drawback with such types of kiln is that treatment of the material cannot be modified during firing so as to produce particular effects, for example, such as those requiring special types of controlled atmosphere.
Accordingly, the object of the invention is to overcome the drawbacks and shortcomings discernable in prior art kilns as described above.